Fine Metal Masks (simply referred to as FMMs) are commonly used in evaporation processes during the manufacturing processes of Organic Light-Emitting Diodes (simply referred to as OLEDs).
FIG. 1a is a partial plan view of a FMM in the prior art, and FIG. 1b is a section view of FIG. 1a, taken along an A-A direction. As shown in FIG. 1a and FIG. 1b, the FMM includes opening regions 1 and shielding regions 2. The opening regions 1 are used for forming any one of a red electroluminescent layer, a green electroluminescent layer and a blue electroluminescent layer, while the shielding regions 2 is used for shielding the other two electroluminescent layers. For example, in a case where the opening regions 1 are used for forming the red electroluminescent layer (Emission layer, EML for short), the shielding regions 2 correspond to positions where the green electroluminescent layer and the blue electroluminescent layer are located. The sectional shape, taken along the A-A direction, of the shielding region 2 is set to be isosceles trapezoid, and the width of the bottom surface of the isosceles trapezoid is D1=b+2a=b+2d/tan θ, so that the dot pitch D=D1+D2≈1.5*D1=1.5(b+2d/tan θ), where θ is the slope angle of the opening region 1, b is the width of the upper surface of the isosceles trapezoid and is generally set to be a fixed value due to the limitations of process conditions, and d is the thickness of the FMM. On the other hand, the dot pitch D is three times as long as pixel pitch D′, that is, D=3*D′, so that the width of shielding region D1≈3*D1′/1.5=2*D′ in the prior art. In such a case, the degree of θ affects the result of evaporation. However, θ is generally set to be 40 to 60 degrees and b is set to be a fixed value due to the limitations of process conditions, and therefore, if it is required to obtain a small pixel pitch D′, the thickness d of the FMM is required to be small. As pixels per inch (PPI for short) is 8.47/D′, if it is required to obtain a higher PPI, the pixel pitch D′ is required to be small, that is to say, the thickness d of the FMM is required to be small. At present, however, the thickness of a metal sheet used for manufacturing a FMM is usually 40 μm, and 30 μm at minimum. Even if a FMM is manufactured by using the metal sheet with the minimum thickness, the pixel pitch D′ thereof cannot meet the requirement of being small, and thus, the higher PPI cannot be obtained.
In the prior art, in a case where the electroluminescent layer of one color is manufactured, because only one FMM is used in evaporation process, all the opening regions used for forming all the patterns in the electroluminescent layer of the one color are required to be manufactured on the one FMM. Taking that a red electroluminescent layer is manufactured as an example, the red electroluminescent layer includes a plurality of red electroluminescent sub-patterns and thus the FMM is a red pattern mask 3. FIG. 1c is a schematic diagram illustrating the formation of the red electroluminescent layer in the prior art and FIG. 1d is a partial plan view of the red pattern mask 3 in the FIG. 1c. As shown in FIG. 1c and FIG. 1d, the red pattern mask 3 is provided above a base substrate 12, and then all of the red electroluminescent sub-patterns 4 are formed on the base substrate 12 by an evaporation process, so that the red electroluminescent layer is formed. The red pattern mask 3 is provided thereon with opening regions 5 used for forming the red electroluminescent sub-patterns 4. As all of the red electroluminescent sub-patterns 4 included in the red electroluminescent layer may be formed by using one red pattern mask 3 and by one evaporation process in the prior art, so that the red pattern mask 3 includes all of the opening regions 5 used for forming all of the red electroluminescent sub-patterns 4. Therefore, the widths of shielding regions 6 between opening regions 5 are required to be small. As the number of opening regions arranged on one FMM is large, the widths of the shielding regions between the opening regions are required to be small when a large number of the opening regions are manufactured, that is to say, the thickness of the FMM is required to be small.
In the current process level of the art, in a case where a thinner metal plate is used for manufacturing the above FMM, the widths of the opening regions cannot remain the same as each other, so that the distribution of the opening regions cannot be uniform, and the product yield is also decreased.
As described above, in the current process level of the art, the thickness of a FMM cannot be manufactured to be thinner (that is, the thickness cannot be smaller than 30 μm). Meanwhile, in order to ensure the product yield and to prevent the FMM from presenting non-uniform distribution of the opening regions, the thickness of a FMM cannot be manufactured to be thin. Therefore, in the current process level of the art, FMM is usually manufactured by using thick metal sheet, so that the PPI of product is decreased and the display definition of the product is also decreased.